An element, in which a Peltier effect or a Seebeck effect is utilized, is used as a thermoelectric conversion element. Recently, because the thermoelectric conversion element has simple-structure and, easy-to-handle, and can maintain a stable characteristic, applications of the thermoelectric conversion element are attracting attention in a wide range of fields. Particularly, when used as an electronic cooling element, the thermoelectric conversion element can perform local cooling and accurate control around room temperature. Therefore, a wide range of studies are being performed to stabilize temperatures of an optoelectronic device, a semiconductor laser, and the like.
As illustrated in FIG.7, in a configuration of a thermoelectric module used in the electronic cooling or thermoelectric generation, a PN element pair is formed such that P-type thermoelectric conversion element (hereinafter, also referred to as “P-type element”) 101 and N-type thermoelectric conversion element (hereinafter, also referred to as “N-type element”) 102 are connected with connection electrode 601 interposed therebetween, and the plural PN element pairs are arrayed in series. Depending on a direction of a current passed through the PN element pair, one end of each of P-type element 101 and N-type element 102 is heated while the other end is cooled. In FIG. 7, the reference signs 602 and 603 designate external connection terminals, the reference sign 604 designates a ceramic board, and the reference sign H designates an arrow indicating the direction of a heat flow.
A material having a large performance index Z (=α2/ρK), which is expressed by a Seebeck coefficient “α” which is of a constant unique to a substance, a specific resistance “ρ” and thermal conductivity “K”, in an operating temperature range is used for the thermoelectric conversion element. A crystalline material of a Bi2Te3 alloy is generally used as the thermoelectric conversion element (for example, see PTL 1).
Usually a fluid is used to heat and cool the PN element pair of the thermoelectric conversion module to facilitate heat transport. For example, the thermoelectric conversion module is disposed on an outer circumferential wall surface of a tube in which a fluid having a temperature different from a temperature outside of the tube flows, which allows an electric power to be generated by a temperature difference between the inside and outside of the tube.
FIG. 8 illustrates a basic structure of a conventional tubular thermoelectric conversion module. The tubular thermoelectric conversion module includes a pair of stacked elements. Each of the stacked elements includes polymer material layer (board) 501, P-type element 101, N-type element 102, and connection electrode 301 that electrically connects P-type element 101 and N-type element 102 in series. Polymer material layers 501 of two stacked elements are bonded by adhesive resin 502. The bonded stacked elements are wound into a spiral or circular shape. P-type element 101 and N-type element 102 are soldered to connection electrode 301 (for example, see PTL 2).
FIG. 9 illustrates another basic structure of the conventional tubular thermoelectric conversion module. Tubular thermoelectric conversion module 401 includes insulating board 403, which includes an inside board that can abut on an outer circumferential surface of metallic tube 402 and an outside board that is bonded to the inside board, thermoelectric conversion elements 411 to 414, 421 to 424, 431 to 434, . . . , and 4m1 to 4m4 that are disposed in through-holes of insulating board 403, surface connection electrode 404X and backside connection electrode 404Y that connect end portions of the thermoelectric conversion element, and leads 404a and 404b that are connected to thermoelectric conversion elements 411 and 414. One end of each of thermoelectric conversion elements 411 to 4m4 is exposed to a surface of the inside board while the other end is exposed to a surface of the outside board.
Each of thermoelectric conversion element 411 to 4m4 includes a P-type element and an N-type element. The P-type elements and the N-type elements are alternately arrayed in a circumferential direction and an axial direction of metallic tube 402. For example, the reference sign 411 designates the P-type element, and the reference sign 414 designates the N-type element. The reference sign 421 designates the N-type element, and the reference sign 431 designates the P-type element. The P-type and N-type elements are alternately arrayed to form a matrix pattern as a whole. The end portion of the P-type element exposed to the inside board and the end portion of the N-type element exposed to the inside board are connected by backside connection electrode 404Y. On the other hand, the N-type element and the P-type element, which are exposed to the outside board of insulating board 403, are connected by surface connection electrode 404X. Therefore, all the thermoelectric conversion elements from P-type element 411 to N-type element 414 are electrically connected in series (for example, see PTL 3).
There is also well known a thermoelectric conversion module in which the thermoelectric conversion elements or a thermoelectric conversion element groups, in each of which the thermoelectric conversion elements are electrically connected in series or parallel, are electrically connected in series by a flexible electrode member. For example, there is well known a thermoelectric conversion module in which the thermoelectric conversion elements are electrically connected in series by a stretchable, fibrous electrode member (for example, see PTL 4).
There is also known a thermoelectric conversion module in which the thermoelectric conversion elements or the thermoelectric conversion element groups, which are supported by a flexible board, are electrically connected in series by the flexible electrode member such as a metallic mesh and a plain stitch wire (for example, PTLs 5 to 8). There is well known a thermoelectric conversion module in which electrodes disposed at both ends of the thermoelectric conversion elements are coupled by the plain stitch wire or a metallic tape to electrically connect the thermoelectric conversion elements in series. There is well known a thermoelectric conversion module in which the thermoelectric conversion elements, which are bonded through a glass sheet interposed therebetween, are electrically connected in series by a wire (for example, see PTLs 9 and 10).
There is well known a thermoelectric conversion module in which plural series circuits of the thermoelectric conversion elements supported by the board are connected in parallel. For example, there is well known a thermoelectric conversion module in which the thermoelectric conversion element is disposed in a hole made in each of the stacked boards, the thermoelectric conversion elements are electrically connected in series to form the series circuit, and the plural series are electrically connected in parallel (for example, see PTLs 11 and 12). There is well known a thermoelectric conversion module in which the series circuits of the thermoelectric conversion elements formed in plural doughnut-shaped boards are electrically connected in parallel and a tube a heat source is inserted in the hole made in the board (for example, see PTLs 13 and 14).
There is well known a thermoelectric conversion module in which the thermoelectric conversion element groups accommodated in a housing or the chip-shaped thermoelectric conversion element groups are electrically connected in parallel (for example, see PTLs 15 to 18).